Register new account on our forums (link).
Confirm registration via link in your email account.
Log in using your username and password (link).
Click on + Create in the upper right hand side corner and click on Game Account (link).
Activate game account via link in your email account.
Download Gracia Epilogue client (link).
Unpack archive using 7Zip (link).
Install client. Don't delete anything!
Download L2 Shrine launcher (link).
Copy launcher into the folder with Gracia Epilogue client (usually C:\Pro